Power is a limited resource in a handheld mobile communication device. Therefore, there is a continuous need to reduce power consumption in such mobile communication devices.
At the same time, due to an increased need for higher data rates and good performance in high load cellular systems, there is a continuous need for improving the modem performance. The modem can be split into three major parts with respect to power consumption, namely the transmitter, receiver and digital baseband sections. The analog transmitter part typically dominates the power consumption in the case of a high transmit power (for example greater than 15 dBm), which typically occurs at the cell coverage border, or when high uplink data rates are needed. The digital baseband part is typically significant only when receiving and decoding very high data rates (for example greater than 10 Mb/s). Finally, the receiver tends to be the part that is typically on for longer periods than the transmitter, both in the case of low and high data rates, and therefore due to the utilization time, is a large contributor to the overall power consumption in a mobile terminal.
FIG. 1 shows an exemplary telecommunications network 10, for example the Evolved Universal Mobile Telecommunications System terrestrial radio access network (E-UTRAN) which uses the Long Term Evolution (LTE) standard. The system 10 comprises a plurality of radio base stations (also known as eNodeBs, NodeBs, etc) 12a, 12b, 12c, each of which maintains one or more cells (not illustrated). User Equipment (UEs) 14a, 14b, 14c, 14d within each cell communicate with a corresponding radio base station 12 of that cell.
In E-UTRAN, radio base stations are capable of communicating with one another over interfaces known as X2 interfaces (illustrated as dashed lines in FIG. 1). Each radio base station 12 further has one or more interfaces with the core network. These are known as S1 interfaces (illustrated as solid lines in FIG. 1). In particular, the radio base stations 12 have one or more interfaces to one or more mobility management entities (MMES) 16a, 16b (known as S1-MME interfaces). As will be appreciated by a person skilled in the art, the telecommunications network 10 will include other nodes and interfaces not shown, including (but not limited to) nodes such as Serving Gateways (S-GWs), Packet Data Network Gateways (PDN-GWs), Serving GPRS Support Nodes (SGSNs) and Home Subscriber Servers (HSSs), plus interfaces such as S1-U, S5, S6a, S3, and so forth.
UEs in a LTE telecommunications network can be in one of two main operating modes or connections states, a Radio Resource Control (RRC) idle mode (RRC_IDLE) or a RRC connected mode (RRC_CONNECTED). In the RRC_IDLE mode, a UE is not known on a cell level but rather on a much larger routing area level. This mode is very energy efficient as the UE does not need to perform handovers, and only needs to read a paging channel from time to time, but no other control channels.
The transitions to lower energy consuming states in a UE receiver occur when the network changes operating mode from one connection state to another. For example, the transitions of power consumption can be controlled on the transitions from a CELL_DCH state to a CELL_FACH state, a transition from a CELL_FACH state to a CELL_PCH state, and a transition from a CELL_PCH state to an idle mode in HSPA.
In order to handle bursty traffic scenarios (for example IP traffic), telecommunication networks utilize different timers for when and how long a UE needs to listen and decode a (typically shared) control channel. When in a RRC_CONNECTED mode in LTE, or a CELL_DCH mode in a High Speed Packet Access (HSPA) network, for example, a UE may be configured to operate in a Discontinuous Reception (DRX) mode of operation as shown in FIG. 2. A DRX cycle may be set at 320 ms, for example. An on-timer T1, for example set to 5 ms, specifies how long during each DRX cycle the UE must decode the control channel, for example the Physical Downlink Control Channel (PDCCH) in LTE as shown, (or the High Speed Shared Control Channel (HS-SCCH) in HSPA). An inactivity-timer T2, for example set to 100 ms, specifies how long the UE must decode the control channel after the last packet is received. If the inactivity-timer expires without the receiver having detected a further packet, then the UE receiver changes its state, from where the receiver in on to where the UE receiver is off until the next DRX period, thus saving power. This may occur for example in the LTE connection state RRC_CONNECTED. It will be appreciated that the inactivity-timer T2 is not used if no packet is sent to the UE.
While such solutions enable UE power savings by turning off the receiver in a connected state of a telecommunication protocol, they have the disadvantage of not fully utilizing the possibilities for power consumption reduction in the radio receiver.
In particular, some of the timers mentioned above are used and set in order to ensure that no delayed packets will be missed, which typically means that they are designed based on worst case delay scenarios that may rarely happen in practice. Examples of such known systems are disclosed in EP2148519, WO2008/054103, US2008/181127 and WO2008/086532.